Chronic beryllium disease (CBD) is a debilitating, progressive lung disease that leads to fibrosis and death. CBD remains an important public health concern with more than 1 million workers at risk. It is characterized by granulomatous inflammation that is mediated by beryllium (Be)-specific CD4+ T cells in the lung. The development of a Be-specific CD4+ T cell response depends on presentation of Be to T cells by MHCII molecules, and the majority of Be-specific CD4+ T cells recognize Be in an HLA-DP-restricted manner. In a novel preclinical model, HLA-DP2 transgenic (Tg) mice exposed to Be generate Be-specific CD4+ T cell responses and granulomatous inflammation in the lung in the absence of added adjuvant. Be also has potent adjuvant effects, and we hypothesize that Be stimulates innate pathways that drive generation of Be-specific CD4+ T cells and CBD. Our preliminary data show that after pulmonary exposure to Be, cell death occurs, and DNA is released into the lung. Monocytes and neutrophils are rapidly recruited to the lung, and classical dendritic cells (cDCs) accumulate in the lung-draining lymph nodes (LDLNs). In C57BL/6 mice, Be exposure enhances priming of CD4+ T cells to bystander antigens through innate pathways. In MyD88-deficient and DNase-treated WT mice, the Be-induced effects on bystander CD4+ T cell responses are impaired. The adjuvant effect of Be on CD4+ T cell responses is intact in mice that lack TLR2, TLR4, TLR7, Nlrp3, Caspase-1 and IL-1R. However in Be-exposed TLR9KO mice, accumulation of cDCs in the LDLNs is impaired, suggesting that TLR9 participates in the MyD88-dependent effects. However, multiple DNA sensors may be involved, because the adjuvant effects of Be on CD4+ T cells are not fully impaired in Be-exposed TLR9KO mice. cDC activation and adequate costimulation are likely critical checkpoints that control the generation of a pathological Be-specific CD4+ Th1 effector response and CBD. Accordingly, targeting these pathways in cDCs may impact disease severity. Our central hypothesis is that Be-induced DNA binds to DNA-sensing receptors in the lung, enhancing cDC function and driving the development of the Be-specific CD4+ Th1 response and that targeting these pathways will ameliorate lung disease in CBD. In Aim 1, we will formally test the role of cDCs and monocytes in the generation of Be-specific CD4+ T cell responses in HLA-DP2 Tg mice. In Aim 2, we will determine the role of DNA-induced innate signaling pathways in the adjuvant effects of Be on cDCs and CD4+ T cell responses. In Aim 3, we will analyze the effects of required innate receptor pathways in driving Be- specific CD4+ T cell responses and lung pathology in the novel HLA-DP2 Tg mouse model of CBD. These studies will fill a critical knowledge gap in our understanding of the link between Be-induced activation of innate and adaptive arms of the immune system that hopefully will lead to new therapeutic targets, particularly in a disease with limited treatments options.